Coating material for pattern fineness enhancement and method of forming fine pattern with the same

ABSTRACT

It is disclosed an over-coating agent for forming fine patterns which is applied to cover a substrate having photoresist patterns thereon and allowed to shrink under heat so that the spacing between adjacent photoresist patterns is lessened, with the applied film of the over-coating agent being removed substantially completely to form fine patterns, further characterized by containing (a) a water-soluble polymer and (b) a water-soluble crosslinking agent having at least one nitrogen atom in its structure. Also disclosed is a method of forming fine-line patterns using the over-coating agent. According to the invention, one can obtain fine-line patterns which exhibit good profiles while satisfying the characteristics required of semiconductor devices, being excellent in controlling the dimension of patterns.

TECHNICAL FIELD

This invention relates to an over-coating agent for forming finepatterns in the field of photolithographic technology and a method offorming fine-line patterns using such agent. More particularly, theinvention relates to an over-coating agent for forming or definingfine-line patterns, such as hole patterns and trench patterns, that canmeet today's requirements for higher packing densities and smaller sizesof semiconductor devices.

BACKGROUND ART

In the manufacture of electronic components such as semiconductordevices and liquid-crystal devices, there is employed thephotolithographic technology which, in order to perform a treatment suchas etching on the substrate, first forms a film (photoresist layer) overthe substrate using a so-called radiation-sensitive photoresistcomposition which is sensitive to activating radiations, then performsexposure of the film by selective illumination with an activatingradiation, performs development to dissolve away the photoresist layerselectively to form an image pattern (photoresist pattern), and forms avariety of patterns including contact providing patterns such as a holepattern and a trench pattern using the photoresist pattern as aprotective layer (mask pattern).

With the recent increase in the need for higher packing densities andsmaller sizes of semiconductor devices, increasing efforts are beingmade to form sufficiently fine-line patterns and submicron-electronicfabrication capable of forming patterns with linewidths of no more than0.20 μm is currently required. As for the activating light raysnecessary in the formation of mask patterns, short-wavelength radiationssuch as KrF, ArF and F₂ excimer laser beams and electron beams areemployed. Further, active R&D efforts are being made to find photoresistmaterials as mask pattern formers that have physical properties adaptedto those short-wavelength radiations.

In addition to those approaches for realizing submicron-electronicfabrication which are based on photoresist materials, from view point ofan increase in a photoresist material life by making improvements toprocesses of forming patterns using existing photoresist materials,active R&D efforts are also being made on the basis of pattern formingmethod with a view to finding a technology that can provide higherresolutions than those possessed by photoresist materials.

For example, JP-5-166717A discloses a method of forming fine patternswhich comprises the steps of defining patterns (=photoresist−uncoveredpatterns) into a pattern-forming resist on a substrate, then coatingover entirely the substrate with a mixing generating resist that is tobe mixed with said pattern-forming resist, baking the assembly to form amixing layer on both sidewalls and the top of the pattern-formingresist, and removing the non-mixing portions of said mixing generatingresist such that the feature size of the photoresist-uncovered patternis reduced by an amount comparable to the dimension of said mixinglayer. JP-5-241348 discloses a pattern forming method comprising thesteps of depositing a resin, which becomes insoluble in the presence ofan acid, on a substrate having formed thereon a resist patterncontaining an acid generator, heat treating the assembly so that theacid is diffused from the resist pattern into said resin insoluble inthe presence of an acid to form a given thickness of insolubilizedportion of the resist near the interface between the resin and theresist pattern, and developing the resist to remove the resin portionthrough which no acid has been diffused, thereby ensuring that thefeature size of the pattern is reduced by an amount comparable to thedimension of said given thickness.

However, in these methods, it is difficult to control the thickness oflayers to be formed on the sidewalls of resist patterns. In addition,the in-plane heat dependency of wafers is as great as ten-odd nanometersper degree Celsius, so it is extremely difficult to keep the in-planeuniformity of wafers by means of the heater employed in currentfabrication of semiconductor devices and this leads to the problem ofoccurrence of significant variations in pattern dimensions. Furthermore,defects (in patterns) due to the formation of the mixing layer are aptto occur, and that these problems are quite difficult to solve.

Another approach known to be capable of reducing pattern dimensions isby fluidizing resist patterns through heat treatment and the like. Forexample, JP-1-307228A discloses a method comprising the steps of forminga resist pattern on a substrate and applying heat treatment to deformthe cross-sectional shape of the resist pattern, thereby defining a finepattern. In addition, JP-4-364021A discloses a method comprising thesteps of forming a resist pattern and heating it at around its softeningtemperature to fluidize the resist pattern, thereby changing thedimensions of its resist pattern to form or define a fine-line pattern.

In these methods, the wafer's in-plane heat dependency is only a fewnanometers per degree Celsius and is not very problematic. On the otherhand, it is difficult to control the resist deformation and fluidizingon account of heat treatment, so it is not easy to provide a uniformresist pattern in a wafer's plane.

An evolved version of those methods is disclosed in JP-7-45510A and itcomprises the steps of forming a resist pattern on a substrate, forminga stopper resin on the substrate to prevent excessive thermal fluidizingof the resist pattern, then applying heat treatment to fluidize theresist so as to change the dimensions of its pattern, and thereafterremoving the stopper resin to form or define a fine-line pattern. As thestopper resin, specifically, polyvinyl alcohol is employed. However,polyvinyl alcohol is not highly soluble in water and cannot be readilyremoved completely by washing with water, introducing difficulty informing a pattern of good profile. The pattern formed is not completelysatisfactory in terms of stability over time.

JP 2001-281886A discloses a method comprising the steps of covering asurface of a resist pattern with an acidic film made of a resist patternsize reducing material containing a water-soluble resin, rendering thesurface layer of the resist pattern alkali-soluble, then removing saidsurface layer and the acidic film with an alkaline solution to reducethe feature size of the resist pattern. JP-2002-184673A discloses amethod comprising the steps of forming a resist pattern on a substrate,then forming a film containing a water-soluble film forming component onsaid resist pattern, heat treating said resist pattern and film, andimmersing the assembly in an aqueous solution of tetramethylammoniumhydroxide, thereby forming a fine-line resist pattern without involvinga dry etching step. However, both methods are simply directed toreducing the size of resist trace patterns themselves and therefore aretotally different from the present invention in object.

DISCLOSURE OF INVENTION

The present invention aims at providing an over-coating agent whichmakes it possible, particularly in the case of forming fine patternswith the use of an over-coating agent, to achieve a favorable ability tocontrol pattern dimensions so as to provide fine patterns whilesustaining the focus margin and give fine-line patterns that have asatisfactory profile and satisfy the characteristics required insemiconductor devices, and a method of forming fine patterns using thesame.

In order to solve the above-described problems, the present inventionprovides an over-coating agent for forming fine patterns which isapplied to cover a substrate having photoresist patterns thereon andallowed to shrink under heat so that the spacing between adjacentphotoresist patterns is lessened, with the applied film of theover-coating agent being removed substantially completely to form finepatterns, further characterized by containing (a) a water-solublepolymer and (b) a water-soluble crosslinking agent having at least onenitrogen atom in its structure.

In a preferred embodiment, component (a) is at least one member selectedfrom among acrylic polymers, vinyl polymers and cellulosic polymers.

In a preferred embodiment, component (b) is at least one member selectedfrom among triazine derivatives, glycoluril derivatives and ureaderivatives.

The present invention further provides a method of forming fine-linepatterns which comprises coating a substrate having photoresist patternswith the above-described over-coating agent for forming fine-linepatterns, applying a heat treatment to cause thermal shrinkage of theover-coating agent, thus lessening the spacing between adjacentphotoresist patterns by the resulting thermal shrinkage action, and thensubstantially completely removing the over-coating agent for formingfine-line patterns.

In a preferred embodiment, the heat treatment is performed by heatingthe substrate at a temperature that does not cause thermal fluidizing ofthe photoresist patterns on the substrate.

BEST MODE FOR CARRYING OUT THE INVENTION

The over-coating agent of the invention for forming fine features ofpatterns is used to be applied to cover a substrate, having photoresistpatterns (mask patterns) thereon, including patterns typified by holepatterns or trench patterns, each of these patterns are defined byspacing between adjacent photoresist patterns (mask patterns). Uponheating, the applied film of over-coating agent shrinks to increase thewidth of each of the photoresist patterns, thereby narrowing orlessening adjacent hole patterns or trench patterns as defined byspacing between the photoresist patterns and, thereafter, the appliedfilm is removed substantially completely to form or define finepatterns.

The phrase “removing the applied film substantially completely” as usedherein means that after lessening the spacing between adjacentphotoresist patterns by the heat shrinking action of the appliedover-coating agent, said film is removed in such a way that nosignificant thickness of the over-coating agent will remain at theinterface with the photoresist patterns. Therefore, the presentinvention does not include methods in which a certain thickness of theover-coating agent is left intact near the interface with thephotoresist pattern so that the feature size of the pattern is reducedby an amount corresponding to the residual thickness of the over-coatingagent.

The over-coating agent of the invention for forming fine patternscontains (a) a water-soluble polymer and (b) a water-solublecrosslinking agent having at least one nitrogen atom in its structure.

The water-soluble polymer as component (a) may be any polymer that candissolve in water at room temperature and various types may be employedwithout particular limitation; preferred examples include acrylicpolymers, vinyl polymers and cellulosic polymers.

Exemplary acrylic polymers include polymers and copolymers havingmonomeric components, such as acrylic acid, methyl acrylate, methacrylicacid, methyl methacrylate, N,N-dimethylacrylamide,N,N-dimethylaminopropylmethacrylamide,N,N-dimethylaminopropylacrylamide, N-methylacrylamide, diacetoneacrylamide, N,N-dimethylaminoethyl methacrylate, N,N-diethylaminoethylmethacrylate, N,N-dimethylaminoethyl acrylate, acryloylmorpholine, etc.

Exemplary vinyl polymers include polymers and copolymers havingmonomeric components, such as N-vinylpyrrolidone, vinyl imidazolidinone,vinyl acetate, etc.

Exemplary cellulosic polymers include hydroxypropylmethyl cellulosephthalate, hydroxypropylmethyl cellulose acetate phthalate,hydroxypropylmethyl cellulose hexahydrophthalate, hydroxypropylmethylcellulose acetate succinate, hydroxypropylmethyl cellulose,hydroxypropyl cellulose, hydroxyethyl cellulose, cellulose acetatehexahydrophthalate, carboxymethyl cellulose, ethyl cellulose,methylcellulose, etc.

Among all, acrylic polymers are most preferable in view of easiness inpH adjustment. It is also preferable a copolymer of an acrylic polymerwith a water-soluble polymer other than acrylic polymers (for example, avinyl polymer or a cellulosic polymer as cited above), since such acopolymer contributes to the improvement in the efficiency of shrinkingthe spacing between adjacent photoresist patterns while maintaining thephotoresist pattern shape during the heat treatment. Either one or morewater-soluble polymers may be used as component (a).

In the case of using a copolymer as component (a), the composition ratioof the constituents of the copolymer is not particularly restricted.Considering stability over time, it is preferable to employ the acrylicpolymer at a higher ratio than other constitutional polymer(s). Inaddition to the above-described way of using the acrylic polymer in alarger amount, it is also possible to improve the stability over time byadding an acidic compound such as p-toluenesulfonic acid ordodecylbenzenesulfonic acid.

To attain a necessary and sufficient film thickness, the content ofcomponent (a) in the over-coating agent (in terms of solid matters) ofthe present invention preferably ranges about 1-99 mas %, stillpreferably about 40-99 mass % and particularly preferably about 65-99mass %.

The water-soluble crosslinking agent as component (b) has at least onenitrogen atom in its structure. As such a water-soluble crosslinkingagent, it is preferable to use nitrogen-containing compounds havingamino and/or imino groups in which at least two hydrogen atoms aresubstituted by hydroxyalkyl and/or alkoxyalkyl groups. Examples of thesenitrogen-containing compounds include melamine derivatives, ureaderivatives, guanamine derivatives, acetoguanamine derivatives,benzoguanamine derivatives and succinylamide derivatives in whichhydrogen atoms in an amino group are substituted by a methylol group, analkoxymethyl group or both of them, and glycoluril derivatives andethyleneurea derivatives in which hydrogen atoms in an imino group aresubstituted.

These nitrogen-containing compounds can be obtained by, for example,reacting melamine derivatives, urea derivatives, guanamine derivatives,acetoguanamine derivatives, benzoguanamine derivatives, succinylamidederivatives, glycoluril derivatives, ethyleneurea derivatives, etc. withformalin in boiling water to convert into methylol-carrying compounds,optionally followed alkoxylation by reacting with lower alcohols, suchas methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol,etc.

Among these nitrogen-containing compounds, it is preferable from theviewpoint of crosslinkability to use benzoguanamine derivatives,guanamine derivatives, melamine derivatives, glycouril derivatives andurea derivatives having an amino group or an imino group in which atleast two hydrogen atoms are substituted by a methylol group, a (loweralkoxy) methyl group or both of them. It is particularly preferable touse triazine derivatives, such as benzoguanamine derivatives, guanaminederivatives or melamine derivatives. It is still preferable that thesetriazine derivatives have 3 or more but less than 6 methylol or (loweralkoxy) methyl groups on average per triazine ring.

Specific examples of such nitrogen-containing compounds includebenzoguanamine derivatives, such as methoxymethylated benzoguanaminehaving 3.7 methoxymethyl groups on average per triazine ring which ismarketed under the trade name “MX-750”, benzoguanamine which is marketedunder the trade name “SB-203” and isobutoxymethylated benzoguanaminewhich is marketed under the trade name “BX-55H” (each product of SanwaChemical Co., Ltd.) and methokymethylated ethoxymethylatedbenzoguanamine which is marketed under the trade name “Cymel 1125”(product of Mitsui Cyanamid Co.) and melamine derivatives such asmethoxymethylated melamine which is marketed under the trade name“MX-788” (product of Sanwa Chemical Co., Ltd.) and methoxymethylatedisobutoxymethylated melamine which is marketed under the trade name“Cymel 1141” (product of Mitsui Cyanamid Co.). As examples of theglycoluril derivatives, methylol glycoluril which is marketed under thetrade name “Cymel 1172” (product of Mitsui Cyanamid Co.), etc. may becited.

The content of component (b) in the over-coating agent (in terms ofsolid matters) of the present invention preferably ranges about 1-99mass %, still preferably about 1-60 mass % and particularly preferablyabout 1-35 mass %.

The over-coating agent of the invention for forming fine patterns ispreferably used as an aqueous solution at a concentration of 3-50 mass%, more preferably at 5-20 mass %. If the concentration of the aqueoussolution is less than 3 mass %, poor coverage of the substrate mayresult. If the concentration of the aqueous solution exceeds 50 mass %,there is no appreciable improvement in the intended effect thatjustifies the increased concentration and the solution cannot be handledefficiently.

As already mentioned, the over-coating agent of the invention forforming fine patterns is usually employed as an aqueous solution usingwater as the solvent. A mixed solvent system comprising water and analcoholic solvent may also be employed. Exemplary alcoholic solventsinclude methyl alcohol, ethyl alcohol, propyl alcohol, isopropylalcohol, glycerol, ethylene glycol, propylene glycol, 1,2-butyleneglycol, 1,3-buthylene glycol, and 2,3-buthylene glycol, etc. Thesealcoholic solvents are mixed with water in amounts not exceeding about30 mass %.

In addition to components (a) and (b), the over-coating agent forforming fine patters of the present invention may optionally containwater-soluble amines and surfactants.

Exemplary water-soluble amines include amines having pKa (aciddissociation constant) values of 7.5-13 in aqueous solution at 25° C.Specific examples include the following: alkanolamines, such asmonoethanolamine, diethanolamine, triethanolamine,2-(2-aminoethoxy)ethanol, N,N-dimethylethanolamine,N,N-diethylethanolamine, N,N-dibutylethanolamine, N-methylethanolamine,N-ethylethanolamine, N-butylethanolamine, N-methyldiethanolamine,monoisopropanolamine, diisopropanolamine and triisopropanolamine;polyalkylenepolyamines, such as diethylenetriamine,triethylenetetramine, propylenediamine, N,N-diethylethylenediamine,1,4-butanediamine, N-ethyl-ethylenediamine, 1,2-propanediamine,1,3-propanediamine and 1,6-hexanediamine; aliphatic amines, such astriethylamine, 2-ethyl-hexylamine, dioctylamine, tributylamine,tripropylamine, triallylamine, heptylamine and cyclohexylamine; aromaticamines such as benzylamine and diphenylamine; and cyclic amines, such aspiperazine, N-methyl-piperazine and hydroxyethylpiperazine. Preferredwater-soluble amines are those having boiling points of 140° C. (760mmHg) and above, as exemplified by monoethanolamine and triethanolamine.The addition of water-soluble amines is effective in view of preventingthe occurrence of impurities and adjusting pH values.

If the water-soluble amine is to be added, it is preferably incorporatedin an amount of about 0.1-30 mass %, more preferably about 2-15 mass %,of the over-coating agent (in terms of solids content). If thewater-soluble amine is incorporated in an amount of less than 0.1 mass%, the coating fluid may deteriorate over time. If the water-solubleamine is incorporated in an amount exceeding 30 mass %, the photoresistpattern being formed may deteriorate in shape.

The surfactant is not limited to any particular types, except that itmust exhibit certain characteristics such as high solubility,non-formation of a suspension and miscibility with component (a). Theuse of such surfactants that satisfy these characteristics caneffectively prevent the generation of defects that has been problems inconventional methods, which is considered to be pertinent tomicrofoaming upon applying over-coating materials on the substrate.

Suitable surfactants include N-alkylpyrrolidones, quaternary ammoniumsalts and phosphate esters of polyoxyethylene.

N-alkylpyrrolidones as surfactant are preferably represented by thefollowing general formula (I):

where R₁ is an alkyl group having at least 6 carbon atoms.

Specific examples of N-alkylpyrrolidones as surfactant includeN-hexyl-2-pyrrolidone, N-heptyl-2-pyrrolidone, N-octyl-2-pyrrolidone,N-nonyl-2-pyrrolidone, N-decyl-2-pyrrolidone, N-undecyl-2-pyrrolidone,N-dodecyl-2-pyrrolidone, N-tridecyl-2-pyrrolidone,N-tetradecyl-2-pyrrolidone, N-pentadecyl-2-pyrrolidone,N-hexadecyl-2-pyrrolidone, N-heptadecyl-2-pyrrolidone andN-octadecyl-2-pyrrolidone. Among these, N-octyl-2-pyrrolidone(“SURFADONE LP 100” of ISP Inc.) is preferably used.

Quaternary ammonium salts as surfactant are preferably represented bythe following general formula (II):

where R₂, R₃, R₄ and R₅ are each independently an alkyl group or ahydroxyalkyl group (provided that at least one of them is an alkyl orhydroxyalkyl group having not less than 6 carbon atoms); X⁻ is ahydroxide ion or a halogenide ion.

Specific examples of quaternary ammonium salts as surfactant includedodecyltrimethylammonium hydroxide, tridecyltrimethylammonium hydroxide,tetradecyltrimethylammonium hydroxide, pentadecyltrimethylammoniumhydroxide, hexadecyltrimethylammonium hydroxide,heptadecyltrimethylammonium hydroxide and octadecyltrimethylammoniumhydroxide. Among these, hexadecyltrimethylammonium hydroxide ispreferably used.

Phosphate esters of polyoxyethylene are preferably represented by thefollowing general formula (III):

where R₆ is an alkyl or alkylaryl group having 1-10 carbon atoms; R₇ isa hydrogen atom or (CH₂CH₂O)R₆ (where R₆ is as defined above); n is aninteger of 1-20.

To mention specific examples, phosphate esters of polyoxyethylene thatcan be used as surfactants are commercially available under trade names“PLYSURF A212E” and “PLYSURF A210G” from Dai-ichi Kogyo Seiyaku Co.,Ltd.

The amount of the surfactant is preferably about 0.1-10 mass %, morepreferably about 0.2-2 mass %, of the over-coating agent (in terms ofsolids content). The addition of the surfactant contributes to theimprovement in coating properties, wafer's in-plane uniformity,prevention of the variations in the percent shrinkage of patterns,prevention of the occurrence of microfoaming and defects, etc.

The method of forming fine-line patterns according to the second aspectof the invention comprises the steps of covering a substrate havingphotoresist patterns thereon with the above-described over-coating agentfor forming fine patterns, then applying heat treatment to shrink theapplied over-coating agent under the action of heat so that the spacingbetween adjacent photoresist patterns is reduced, and subsequentlyremoving the applied film of the over-coating agent completely.

The method of preparing the substrate having photoresist patternsthereon is not limited to any particular type and it can be prepared byconventional methods employed in the fabrication of semiconductordevices, liquid-crystal display devices, magnetic heads and microlensarrays. In an exemplary method, a photoresist composition of chemicallyamplifiable or other type is spin- or otherwise coated on a substratesuch as a silicon wafer and dried to form a photoresist layer, which isilluminated with an activating radiation such as ultraviolet,deep-ultraviolet or excimer laser light through a desired mask patternusing a reduction-projection exposure system or subjected to electronbeam photolithography, then heated and developed with a developer suchas an alkaline aqueous solution, typically a 1-10 mass %tetramethylammonium hydroxide (TMAH) aqueous solution, thereby forming aphotoresist pattern on the substrate.

The photoresist composition serving as a material from which photoresistpatterns are formed is not limited in any particular way and any commonphotoresist compositions may be employed including those for exposure toi- or g-lines, those for exposure with an excimer laser (e.g. KrF, ArFor F₂) and those for exposure to EB (electron beams).

Among them, it is preferable to use a photoresist composition whichnever causes the formation of a mixing layer around the interfacebetween the photoresist patterns and the over-coating layer of thepresent invention in the case of forming the photoresist patterns. Whena mixing layer is formed, there are observed undesirable phenomena suchthat defects are likely to arise and that the in-plane heat dependencyof the substrate attains ten-odd nanometers.

In the case of using photoresist compositions for exposure to i- org-lines (for example, positive-working photoresist compositionscontaining a novolac resin and a naphtoquinone diazide-typephotosensitive agent), the above-described problems may never arise andthus it is unnecessary to worry about them. However, in the case ofusing chemical amplification photoresist compositions containing acompound which generates an acid upon light exposure (i.e., an acidgenerator), such as photoresist compositions for exposure to an excimerlaser and photoresist compositions for exposure to EB (electron beams),it should be taken into account that a mixing layer is sometimes formedaround the interface between the over-coating agent and the photoresistpatterns due to the acid generated from the acid generator. Theformation of the mixing layer depends on the diffusion length (diffusiondistance) of the acid generated from the acid generator and the amountsof a basic substance to be added. Therefore, in the case of using aphotoresist composition for exposure to an excimer laser or aphotoresist composition for exposure to EB (electron beams), it isfavorable to select an appropriate photoresist composition forpreventing the formation of such a mixing layer as described above.

After thusly forming the photoresist pattern as a mask pattern, theover-coating agent for forming fine patterns is applied to coverentirely the substrate. After applying the over-coating agent, thesubstrate may optionally be pre-baked at a temperature of 60-150° C. for10-90 seconds.

The over-coating agent may be applied by any methods commonly employedin the conventional heat flow process. Specifically, an aqueous solutionof the over-coating agent for forming fine patterns is applied to thesubstrate by any known application methods including whirl coating witha spinner, etc.

In the next step, heat treatment is performed to cause thermal shrinkageof the film of the over-coating agent. Under the resulting force ofthermal shrinkage of the film, the dimensions of the photoresist patternin contact with the film will increase by an amount equivalent to thethermal shrinkage of the film and, as the result, the photoresistpattern widens and accordingly the spacing between the adjacentphotoresist patterns lessens. The spacing between the adjacentphotoresist patterns determines the diameter or width of the patterns tobe finally obtained, so the decrease in the spacing between the adjacentphotoresist patterns contributes to reducing the diameter of eachelement of hole patterns or the width of each element of trenchpatterns, eventually leading to the definition of a pattern with smallerfeature sizes.

The heating temperature is not limited to any particular value as longas it is high enough to cause thermal shrinkage of the film of theover-coating agent and form or define a fine pattern. Heating ispreferably done at a temperature that will not cause thermal fluidizingof the photoresist pattern. The temperature that will not cause thermalfluidizing of the photoresist pattern is such a temperature that when asubstrate on which the photoresist pattern has been formed but no filmof the over-coating agent has been formed is heated, the photoresistpattern will not experience any dimensional changes (for example,dimensional changes due to spontaneously fluidized deforming).Performing a heat treatment under such temperature conditions is veryeffective for various reasons, e.g. a fine-line pattern of good profilecan be formed more efficiently and the duty ratio in the plane of awafer, or the dependency on the spacing between photoresist patterns inthe plane of a wafer, can be reduced. Considering the softening pointsof a variety of photoresist compositions employed in currentphotolithographic techniques, the preferred heat treatment is usuallyperformed within a temperature range of about 80-160° C. for 30-90seconds, provided that the temperature is not high enough to causethermal fluidizing of the photoresist.

The thickness of the film of the over-coating agent for the formation offine-line patterns is preferably just comparable to the height of thephotoresist pattern or high enough to cover it.

In the subsequent step, the remaining film of the over-coating agent onthe patterns is removed by washing with an aqueous solvent, preferablypure water, for 10-60 seconds. Prior to washing with water, rinsing mayoptionally be performed with an aqueous solution of alkali (e.g.tetramethyl-ammonium hydroxide (TMAH) or choline). The over-coatingagent of the present invention is easy to remove by washing with waterand it can be completely removed from the substrate and the photoresistpattern.

As a result, each pattern on the substrate has a smaller feature sizebecause each pattern is defined by the narrowed spacing between theadjacent widened photoresist patterns.

The fine-line pattern thus formed using the over-coating agent of thepresent invention has a pattern size smaller than the resolution limitattainable by the conventional methods. In addition, it has a goodenough profile and physical properties that can fully satisfy thecharacteristics required of semiconductor devices.

The technical field of the present invention is not limited to thesemiconductor industry and it can be employed in a wide range ofapplications including the fabrication of liquid-crystal displaydevices, the production of magnetic heads and even the manufacture ofmicrolens arrays.

EXAMPLES

The following examples are provided for further illustrating the presentinvention but are in no way to be taken as limiting. Unless otherwisenoted, all amounts of ingredients are expressed in mass %.

Example 1

A copolymer of acrylic acid and vinylpyrrolidone [98 g; acrylicacid/vinylpyrrolidone=2:1 (mass ratio)] andtetra(hydroxymethyl)glycoluril (2 g) were dissolved in water (1900 g) toprepare an over-coating agent having the overall solids content adjustedto 5 mass %.

A substrate was whirl coated with a positive-acting photoresistTDMR-AR2000 (product of Tokyo Ohka Kogyo Co., Ltd.), which contain anovolac resin and a naphtoquinone diazide-type photosensitive agent, andbaked at 90° C. for 90 seconds to form a photoresist layer in athickness of 1.3 μm.

The photoresist layer was exposed with a laser exposure unit (NikonNSR-2205il4E of Nikon Corp.), subjected to heat treatment at 110 ° C.for 90 seconds and developed with an aqueous solution of 2.38 mass %TMAH (tetramethylammonium hydroxide) to form photoresist patterns whichdefined hole patterns with an each diameter of 411.8 nm (i.e., thespacing between the photoresist patterns was 411.8 nm).

Then above-described over-coating agent was applied onto the substrateincluding the hole patterns and subjected to heat treatment at 120° C.for 60 seconds. Subsequently, the over-coating agent was removedcompletely using pure water at 23° C. The each diameter of the holepatterns was reduced to about 231.2 nm.

Example 2

A copolymer of acrylic acid and vinylpyrrolidone [98 g; acrylicacid/vinylpyrrolidone=2:1 (mass ratio)] andtetra(hydroxymethyl)glycoluril (2 g) were dissolved in water (400 g) toprepare an over-coating agent having the overall solids content adjustedto 20 mass %.

A substrate was whirl coated with an excimer laser-ready photoresistcomposition DP-TFOLOPM (product of Tokyo Ohka Kogyo Co., Ltd.), andbaked at 130° C. for 150 seconds to form a photoresist layer in athickness of 3.0 μm.

The photoresist layer was exposed with a laser exposure unit FPA3000EX3(Canon Inc.), subjected to heat treatment at 120° C. for 150 seconds anddeveloped with an aqueous solution of 2.38 mass % TMAH to formphotoresist patterns which defined hole patterns with an each diameterof 202.2 nm (i.e., the spacing between the photoresist patterns was202.2 nm).

Then above-described over-coating agent was applied onto the substrateincluding the hole patterns and subjected to heat treatment at 120° C.for 60 seconds. Subsequently, the over-coating agent was removedcompletely using pure water at 23° C. The each diameter of the holepatterns was reduced to about 138.5 nm.

Example 3

A copolymer of acrylic acid and vinylpyrrolidone [98 g; acrylicacid/vinylpyrrolidone=2:1 (mass ratio)] andtetra(hydroxymethyl)glycoluril (2 g) were dissolved in water (400 g) toprepare an over-coating agent having the overall solids content adjustedto 20 mass %.

A substrate was whirl coated with an electron beam-ready photoresistcomposition EP-TF004EL (product of Tokyo Ohka Kogyo Co., Ltd.), andbaked at 150° C. for 300 seconds to form a photoresist layer in athickness of 2.0 μm.

The photoresist layer was exposed to be traced with an electron beam(EB) lithography equipment (HL-800D of Hitachi, Ltd.), subjected to heattreatment at 140° C. for 300 seconds and developed with an aqueoussolution of 2.38 mass % TMAH to form photoresist patterns which definedhole patterns with an each diameter of 234.8 nm (i.e., the spacingbetween the photoresist patterns was 234.8 nm).

Then above-described over-coating agent was applied onto the substrateincluding the hole patterns and subjected to heat treatment at 120° C.for 60 seconds. Subsequently, the over-coating agent was removedcompletely using pure water at 23° C. The each diameter of the holepatterns was reduced to about 172.6 nm.

Comparative Example 1

Photoresist patterns were formed in the same manner as described inEXAMPLE 1, except that an aqueous solution of 5 mass % polyvinyl alcoholwas used as the over-coating agent. In this case, the over-coating agentcould not be removed completely in the removing step with pure water at23° C., and residues that were visually confirmed remained on thesubstrate.

Comparative Example 2

Photoresist patterns were formed in the same manner as described inEXAMPLE 2, except that the over-coating agent was not used. That is, asdescribed in EXAMPLE 2, the photo-resist layer on the substrate wasdeveloped with an aqueous solution of 2.38 mass % TMAH to formphotoresist patterns which defined hole patterns with an each diameterof 202.2 nm. Then the substrate without being covered with theover-coating agent was subjected to heat treatment at 120° C. for 60seconds. As a result, the each size of the hole patterns did notchanged, and therefore fine-line patterns were not obtained.

INDUSTRIAL APPLICABILITY

As described above in detail, according to the present inventions of theover-coating agent for forming fine-line patterns and the method offorming fine-line patterns using the agent, one can obtain fine-linepatterns which exhibit good profiles, being excellent in controlling thedimension of patterns and in removing the applied film of theover-coating agent, while satisfying the characteristics required ofsemi-conductor devices.

1. An over-coating agent for forming fine patterns which is applied tocover a substrate having photoresist patterns thereon and allowed toshrink under heat so that the spacing between adjacent photoresistpatterns is lessened, with the applied film of the over-coating agentbeing removed substantially completely to form fine patterns, furthercharacterized by containing (a) a water-soluble polymer and (b) awater-soluble crosslinking agent having at least one nitrogen atom inits structure.
 2. The over-coating agent for forming fine patternsaccording to claim 1, wherein component (a) is at least one memberselected from among acrylic polymers, vinyl polymers and cellulosicpolymers.
 3. The over-coating agent for forming fine patterns accordingto claim 1, wherein component (b) is at least one member selected fromamong triazine derivatives, glycoluril derivatives and urea derivatives.4. The over-coating agent for forming fine patterns according to claim1, which is an aqueous solution having a concentration of 3-50 mass %.5. The over-coating agent for forming fine patterns according to claim1, wherein the agent, in terms of solid matters, contains 1-99 mass % ofcomponent (a) and 1-99 mass % of component (b).
 6. The over-coatingagent for forming fine patterns according to claim 1, wherein the agent,in terms of solid matters, contains 40-99 mass % of component (a) and1-60 mass % of component (b).
 7. A method of forming fine patternscomprising the steps of covering a substrate having thereon photoresistpatterns with the over-coating agent for forming fine patterns of claim1, then applying heat treatment to shrink the applied over-coating agentunder the action of heat so that the spacing between adjacentphotoresist patterns is lessened, and subsequently removing the appliedfilm of the over-coating agent substantially completely.
 8. The methodof forming fine patterns according to claim 7, wherein the heattreatment is performed by heating the substrate at a temperature thatdoes not cause thermal fluidizing of the photoresist patterns on thesubstrate.